It is well known that when a passage in which a fluid, such as water or the like, passes through is abruptly closed, there occurs the so-called “water hammer.” The “water hammer” is a pressure effect manifested by the fluid in the passage under these conditions in which the pressure inside the passage vibratingly rises upstream of the place or point where the passage is closed abruptly.
When a water hammer is created, various problems, such as breakdown of devices or instruments connected to the fluid passage, are caused by the vibrating rise of the internal pressure in the upstream side passage.
Therefore, various techniques have been developed to prevent water hammer. However, these techniques basically address the water hammer effect by (1) making the time for closing the fluid passage long (i.e., so closing of the fluid passage is not so abrupt), or (2) by having the vibrating pressure generated inside the passage released to the outside by opening a bypass passage, or (3) by absorbing the water hammer using a separately installed accumulator. The method by which the time for closing the passage is lengthened is undesirably time-consuming with the result that this method can not be applied to situations where there is the need of urgent (or rapid) closing of the fluid passage. On the other hand, the other two methods for avoiding the water hammer necessarily involve attachments to the fluid passage, which adds cost to building a system and to practicing a method for closing a fluid passage without generating a water hammer. The added costs for these attachments is too high.
The water hammer related problems discussed above have arisen previously in industrial fields where the fluid flowing in the passage involved a relatively great flow rate. In recent years, however, avoiding the water hammer effect has become desirable even in fields where the fluid moves with a small flow rate. For example, in the fields of wet type oxide film treatment of silicon in the semiconductor manufacturing industry, or wafer cleaning apparatus development, or the development of chemical liquid supply systems and in the field of medicine production, prevention of water hammer generation during urgent (or prompt) closure of the fluid supply passage has been strongly required in order to maintain the facilities of production, upgrade the product quality, and reduce the opening/closing time of valves in accordance with increased frequency of valve opening/closing.
Examples of prior art devices and methods employed for addressing the problem of the generation of a water hammer include: (a) Patent Document 1 Toku-Kai-Hei No. 7-190235, which describes a valve control device; (b) Patent Document 2 Toku-Kai No. 2000-10602, which describes a PID control method and its controller; and (c) Patent Document 3 Toku-Kai No. 2002-295705, which describes a motor-operated valve for preventing water hammer, and its controlling method.